Nonlinear dynamics of crustal blocks and faults and earthquake occurrences in the Transcaucasian region

Abstract

The Caucasus is a part of ongoing collision of the Arabian and Eurasian plates, where moderate to strong earthquakes caused significant losses of lives and livelihood in the past. To better understand seismic hazard in the region, we develop a model of block-and-fault dynamics for Transcaucasia, the largest part of the Caucasus to the south of the Greater Caucasus Mountains, to simulate regional earthquakes. The model structure is developed by employing the results of the morphostructural analysis to delineate crustal blocks and the geodetic observations on crustal movements in the region. The model incorporates a nonlinear rate-dependent slip of the faults separating the blocks. A set of numerical experiments has been performed to address the following questions: (i) where strong earthquakes occur and what their reoccurrence time is; (ii) how rigid crustal blocks react to the Arabian plate push and to movements of the ductile part of the crust in Transcaucasia; and (iii) whether the fault slip rates and the block displacements in the model correlate with observed GPS-velocities. The model results confirm that the contemporary crustal dynamics and seismicity pattern in Transcaucasia are determined by the north-northeastern motion of the Arabian plate relative to Eurasia and by the movement of the ductile crust underlying the rigid crustal blocks. Variations in the rheological properties of the fault zones and/or of the ductile crust influence the pattern of seismicity. The number and maximum magnitude of synthetic earthquakes change with the variations in the movements of the crustal blocks and in the rheological properties of the lower crust and the fault zones. The model results can be used in comprehensive seismic hazard assessment of the Caucasus region based on instrumentally observed, historical and synthetic seismicity.